Inflatable rubber sleeve type packers have been used for many years in relatively short lengths. The sleeve of these packers has reinforcing ribs which extend continuously along the length of the sleeve which, among other things, prevent portions of the sleeve from moving axially along its supporting mandrel. However, longer versions of these packers do not have continuous ribs in their sleeves resulting in a tendency of the sleeve to move axially along the mandrel while being run into a well resulting in a failure of the sleeve and therefore loss of the sealing and anchoring ability of the packer. Such a loss may require the retrieval of the pipe string upon which the packer has been run, which in turn causes expensive and dangerous delays in the drilling and completion of high pressure oil and gas wells.
Movement of the sleeve axially along the mandrel, before inflation of the sleeve, may be caused by any one of several factors: the pipe string upon which the packer is run may have moved laterally against the side of the borehole; the borehole may not be straight, causing contact of the pipe string with the borehole at three or more levels; the borehole may have cuttings stacked within it so as to force the pipe string to contact the borehole wall; the pipe may be in compression at the packer level and thereby cause the pipe to buckle and to contact the borehole wall. Any one of the above factors, when occuring at a level so as to cause the packer sleeve to be forced against the borehole wall, may cause relative axial movement between the mandrel and the sleeve of the prior art, before the sleeve is inflated. Such axial movement of the sleeve relative to the mandrel has in the past caused the sleeve to tear away from its upper attachment to the mandrel and thereby has prevented the sleeve from providing the intended functions of sealing and anchoring against the borehole. The tendency for a long sleeve to slide along the mandrel is greater than for a short sleeve because of the longer length of contact between the sleeve and the borehole and also because it lacks the continuous ribs found in the short sleeves. It will be appreciated that when a sleeve is forced against the borehole wall and the pipe string is lowered, a tendency for relative movement between the sleeve and the mandrel exists, and that if the mandrel within the sleeve has a smooth outer surface according to the prior art, the borehole wall along the length of the sleeve may easily cooperate with the sleeve, to develop a greater bond than the frictional resistance between the sleeve and the smooth mandrel and thereby cause the sleeve to hold to the borehole wall while the mandrel slides along the sleeve to result in failure of the sleeve. It will also be appreciated that if the exterior surface of the mandrel is made of sufficient roughness according to the present invention, that the frictional bond between the mandrel and the sleeve, before inflation of the sleeve, can be made sufficiently strong so as to cause the sleeve to move along the borehole wall regardless of the sleeve length, which in turn prevents rupture of the sleeve as described above, to preserve the sealing and anchoring capability of the packer.
Therefore, features of the present invention are to:
Provide an inflatable packer sufficiently strong so as to withstand without damage, positioning operations prior to inflation of the packer;
Provide means to prevent rupture of the sleeve of an inflatable packer caused by axial forces thereon;
Provide means to reduce the tendency for relative axial movement between the sleeve and the mandrel before inflation of the sleeve.
Provide a mandrel having an outer surface of increased roughness.